1. Field of the Invention
The present invention relates to a structure for supporting a pulley holder which comprises a pulley holder for rotatably supporting pulleys on which a belt is wound in a state capable of circular movement, a frame member for slidably supporting the pulley holder in a direction of stretching the belt, and an urging member for elastically urging the pulley holder in a tension direction in which the belt is tensioned. More particularly, the present invention relates to a structure for supporting a pulley holder formed in a shape having draft angle as having been molded by molding die. The present invention further relates to a pulley holder supported by such supporting structure.
2. Description of the Related Art
In an image recording apparatus of ink jet type, a driving transmission mechanism for transmitting a driving force to a carriage which is supported in a state capable of sliding movement in a predetermined direction is known (See Japanese Patent Application Laid-open No. 07-293671 (1995) and Japanese Patent Application Laid-open No. 2001-158145). FIG. 1A and FIG. 1B exemplify a driving transmission mechanism 220 employing known pulleys. FIG. 1A is a plan view of the driving transmission mechanism 220 while FIG. 1B is a front view of the same. As shown in FIG. 1A and FIG. 1B, the driving transmission mechanism 220 has a configuration in which a driving pulley unit 233 and a driven pulley unit 223 are mounted on a frame 221 as spaced from each other, and an endless belt 222 is stretched between the two pulley units 233 and 223.
The driving pulley unit 233 is configured by a motor 236 mounted on the lower surface 221b of the frame 221, a motor shaft 235 penetrating from the lower surface 221b through the frame 221 to the upper surface 221a, and a driving pulley 234 coupled to the motor shaft 235. The driven pulley unit 223 is configured by a pulley holder 225 fixedly mounted to the frame 221 and a driven pulley 224. The belt 222 is wound around the driving pulley 234 and the driven pulley 224. By applying rotational force of the driving pulley 234, the belt 222 is conveyed as if it circularly moves between the driving pulley 234 and the driven pulley 224. The belt 222 thus circularly moves is joined to a carriage as described above. As the belt 222 circularly moves, the carriage is moved in a predetermined direction.
FIG. 2A and FIG. 2B are side views showing a configuration of the driven pulley unit 223 of a known driving transmission mechanism. As shown in FIG. 2A and FIG. 2B, the pulley holder 225 is configured mainly by a support arm 229 for rotatably supporting the driven pulley 224, an insertion portion 238 inserted in an insertion opening 241 (See FIG. 4) formed in the frame 221, and a restricting portion 226 for restricting the downward movement of the insertion portion 238. In FIG. 2A and FIG. 2B, a lower portion of the restricting portion 226 beneath the lower surface 226a is the insertion portion 238. The insertion portion 238 has stopper portions 227 protruding perpendicular to the drawing sheet surface of FIGS. 2A and 2B. A pair of grooves 228 are provided between the stopper portions 227 and the restricting portion 226 for engagement with corresponding engaging edges 242 (See FIG. 4) provided at the insertion opening 241 of the frame 221. The pulley holder 225 is inserted with its insertion portion 238 in the insertion opening 241 shown in FIG. 4. By sliding the pulley holder 225 leftwardly in FIG. 4 (denoted by the white arrow), its engaging edges 242 are inserted in the corresponding grooves 228 with contacting each other. As the result, the pulley holder 225 is fixed to the frame 221 in the orthogonal direction with respect to the frame 221. Simultaneously, the pulley holder 225 is retained by a retainer not shown and inhibited from sliding movement to right-left direction in FIG. 2A and FIG. 2B.
When the pulley holder 225 is a molded article made of a synthetic resin, a predetermined draft angle φ is provided for ease of its removing from the cavity of the molding die. FIG. 3 is a cross sectional view taken along the line III-III of FIG. 2B, and FIG. 4 is a plan view showing the insertion opening formed in the frame.
In general, in the synthetic resin molding technique, a draft angles from 0.5° to 2° is provided. Hence, as shown in FIG. 3, the pulley holder 225 is formed in a shape inclining by the angle φ in the direction removing from the cavity of the die. As shown in FIG. 2A and FIG. 2B, since engaging sides 230 which are bottom surfaces of the grooves 228 and to which the draft angle is provided are formed along substantially the entire length of the pulley holder 225. In actuality, surface contact between the engaging edges 242 and the engaging sides 230 does not occur, and only point contact occurs therebetween. Accordingly, the known structure for supporting the pulley holder 225 may fail to ensure a sufficient strength of the pulley holder for supporting the driven pulley 224 with respect to its rotational direction, thus resulting in jerky movements of the driven pulley 224 in the rotational direction of the driven pulley 224. Such problem will interrupt the smooth circular movement of the belt and generate a positional error of the carriage during sliding, hence declining the quality of images recorded by the image recording apparatus.